Can CTS stop tracing on hierarchical module ports?

Hi agruebl,

You need the "LeafPin" command in your ".ctstch" file on the input pin of the first device(s) in your module.

If you look at the "Encounter User Guide" (soceUG.pdf), "Synthesizing Clock Trees" (Chapter 11),
Product Version 6.2.2 (SOC6.2), August 2007, on Page 477, you will see the following:

LeafPin
+ pinName rising | falling
+ …


Marks the input pin as a “leaf” pin for non-clock-type
instances, stops tracing, and balances clock skew.
Note: Use the LeafPin statement only with input pins.
CTS ignores LeafPin statements that are associated
with output pins.

Choose one of the following:
rising - CTS treats the input pin as a risingedge-
triggered flip-flop clock pin.
falling - CTS treats the input pin as a fallingedge-
triggered flip-flop clock pin.

Here's a real life example. These are input pins of devices where clock was stopped
from tracing through combinational logic gates.

LeafPin
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/a1
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/a2
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/b1
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/b2


Regards - R.M.

Hi agruebl,

My previous example should have had the word "rising" at the end of each LeafPin declaration:

LeafPin
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/a1 rising
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/a2 rising
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/b1 rising
+ i_macro/i_core/i_usb_device_top/i_usb_asyn_hand/asyn_hand_ps1/u19/b2 rising


Regards - R.M.

Hi raul63,

many thanks for your answer! Unfortunately it doesn't fix my problem... What I did not mention is that I switch (not regularly but I do ;-) ) between cell libraries and the input pins have different names in the diff. libraries.

So I wanted to have a somewhat technology independent solution and define the module's input port as a leaf. Consequently CTS would have to either:
* automatically treat all directly connected cell inputs (inside the module) as leaf pins, or
* treat the module input as a leaf.

The second point is probably impossible because CTS wouldn't "know" where to stop tracing when using this module port without physical pins. So the question is wether the firts point is feasible.

One (rather time consuming) solution I am currently thinking about is to extract the names of the leaf pins connected to the module port using a TCL script and to insert these names into the ".ctsh" file using a PERL script or something.

Hope this describes my problem a bit more precisely... any ideas? ;-)

Regards,
Andreas

Hi Andreas,

I have never tried what you are attempting to do, however,
in the Encounter User's Guide, there is the following command,
which I am assuming would declare a module port as a "LeafPort":

LeafPort
+ portName rising | falling
+ …

Marks the port as a “leaf” port for non-clock-type
instances, stops tracing, and balances clock skew.
Choose one of the following:
rising CTS treats the pin as a rising-edgetriggered
flip-flop clock pin.
falling CTS treats the pin as a falling-edgetriggered
flip-flop clock pin.


From Encounter User Guide
Synthesizing Clock Trees
August 2007 Product Version 6.2.2, p. 478

Regards - R.M.

Hi Andreas,

You do not need to write a perl script. What you can do is to load the database into FE.
Under the top menu "Tools", open up the design browser, (let say that hierarchical module and port name is
ata_top/atahost1/clk_i),
fill in the name in and click 'Enter', it will show all the instance with pin that connect to this input port.
Save the file using File => Save As.

agruebl:

You can use 'dbGetHTermByName' to get the hierarchical term, and then use 'dbHTermNet' to get the net. Finally use the db command to get all downstream inputs of that net. all you need is to define the module port pattern. And then use some TCL to output the leafpin definitions.

Best Regard

@raul63:
I have tried this but CTS gives the warning

**WARN: The LeafPort + sn_top/rx_delay/rx_del0_0_/in is an invalid name.

for every hierarchical port that I specify (product version 5.2.6). This option seems a bit useless, provided it accepts only top level ports as arguments?

@bsg:
... I'm trying to avoid GUI usage in our design flow (after floorplanning) ;-) Unfortunately some instance names do change after intermediate re-synthesis runs.

@eminemshow:
This seems to exactly solve my problem. But my software doesn't recognize the db commands. Are these OpenAccess commands (not available here)? I couldn't even find them in the SKILL manual..
Anyway, I will try to do this all in TCL using get_pins and all_connected etc. Thanks for the hint!


Thank you all for you help! Great forum! :-)

This is an interesting thread- thanks for raising the question!

Here's some thought I have on what's been discussed:

(1) It looks like CTS doesn't offer an ability to stop on hierarchical module ports.  In some ways, that's not surprising because a hierarchical module port doesn't necessarily have a physical location.  If we're asking the tool to build a tree *to* the module port and it doesn't have a location, how should CTS know where to place the buffers?  The intent may be to treat elements downstream from the hierarchical module port as a leaf (which sounds like what you're seeking to do), but it's not clear to me that everyone would expect this behavior every time.

(2) The leafPort option offers a way to specify a stop point based on the master cell name rather than the instance name (ie, "BUFX1/A" instead of "DTMF_INST/RESUTLS_CONV_INST/i0/A").  With a leafPort, you can therefore be more concise in the way you instruct the tool to stop based on cell-type rather than having to find and list every instance pin.  Hope that makes sense.

(3)  You might want to consider specifying these pins as "ExcludePin" rather than "LeafPin"- the difference being whether CTS balances to the elements inside the module or merely omits them from being sink targets.

(4)  Regarding coming up with a scripted solution to the challenge of "how to find the instance pins driven by a hierarchical module port"- there are 3 options for db access in this area that I'll include examples of below.

Hope this helps

Oops- I forgot to click the "html" tab before posting the code example. Hopefully this will come through readably:

Bob:

I just attended the SOC-E 71 Release seminar. It is great that you give a living example of how to use dbGet.
Many Thanks!

Best Regard